1. Field of the Invention
This invention relates to a water repellent agent for use in treating inorganic materials such as glass, ceramics and metals for imparting water repellency and stain-proofness to their surface. More particularly it relates to a water repellent agent for treating inorganic materials such that the inorganic material surface may be self-cleaning with rain water.
2. Prior Art
Various research endeavors have been made for enhancing the performance and expanding the applicable range of inorganic materials such as glass, ceramics and metals by treating the inorganic materials at their surface with various surface treating agents for improving surface properties. One typical technique is to treat an inherently hydrophilic surface with a silicone composition for modifying the surface to be water repellent.
Japanese Patent Application Kokai (JP-A) Nos. 147484/1983, 221470/1985 (or U.S. Pat. No. 4,678,688) and 96935/1992 disclose that polysiloxane and polysilazanes having a perfluoroalkyl group excel in water repellency. These water repellent agents are excellent in water repellency, but less effective in allowing water droplets to fall down. When they are applied to glazing in houses and buildings as stain-proof treating agents, water droplets tend to stay on the glazing surface as dots instead of falling down. Then the glazing is undesirably stained because dust, debris and oil in the atmosphere can adhere to such water droplets.
Also fluorinated silazane compounds are disclosed in JP-A 290437/1991. Although these compounds eliminate the above-mentioned drawback, they are substantially insoluble in conventional organic solvents. They are soluble only in Freons currently under federal restriction such as 1,1,3-trichlorotrifluoro-ethane and expensive fluorinated hydrocarbons. This limits the application range.